The Treaty of Trianon forced this country to give up three-fourths of its territory.
Hungary
Romania
Austria
Croatia
Yugoslavia
Hungary. The 1920 Treaty of Trianon was forced upon Hungary by the victorious Allies after WWI and resulted in Hungary giving up three-fourths of its territory to Romania, Czechoslovakia and the Kingdom of Serbs, Croat and Slovenes. Hungary lost more than half its population, including some 3 million Hungarians.